Electric furnace method



June 10, 1930. w E, MOORE 1,763,248

ELECTRIC FURNACE METHOD Original Filed June 19, 1928 Patented June 10,1930 UNITED STATES PATENT OFFICE WELIAM E. MOORE, OF PITTSBURGH,PENNSYLVANIA, ASSIGNOR TO PITTSBURGH RESEARCH CORPORATION, OFPITTSBURGH, PENNSYLVANIA ELECTRIC FURNACE METHOD Original applicationfiled June 19, 1928, Serial No. 288,594. Divided and this applicationfiled April 18,

1929. Serial No. 354,603.

This invention relates to metallurgical furnaces and more particularlyto an improved furnace for and method of carburizing metallic charges.

5 It'has heretofore been the common practice to construct the hearth orbottom of are type metallurgical furnaces of refractory material, suchas magnesite, dolomite or ganister, which becomes electricallyconducting at high temperatures. It has also been proposed to constructfurnace bottoms of this kind'of a layer of refractory material which isof progressively increasing conductivity from the top downward.

Such a bottom, however, does not give the best results for certainclasses of work, and I now propose to provide a furnace bottomconsisting of a layer of substantially uniform high conductivitythroughout. I have also found that when treating such metals as iron orsteel for the purpose of carburizing them, it is desirable to form thefurnace bottom or hearth of carbon or carbonaceous material capable ofgiving up carbon to the charge.

The present invention also seeks to provide means for treating thecharge with gas or fluid as well as to facilitate the carburizingthereof by agitating the same while in contact with such a carbonaceousbottom or hearth. In this connection, I have discovered that thecarburizing action can be expedited by treating the charge by fluid orliquid hydrocarbons, and by mixing carbonaceous material with the chargeand then agitating the charge while such material floats upon thesurface thereof.

The present application is a division of my prior application, SerialNo. 286,594 filed June 19, 1928.

a part of this specification and wherein like characters of referencedenote like or corresponding parts throughout the same,

Figure 1 is a view in vertical section of a three phase furnaceconstructed in accord-- ance with the invention, and showing my improvedmeans for agitating the charge, and,

Figure 2 is a fragmentary vertical section In the accompanying drawingswhich form I showing the furnace bottom and a modified means foragitating the charge.

In the drawings wherein for the purpose of illustration is shown apreferred embodiment of my invention, the furnace is designated in itsentirety by the reference numeral 1. This furnace is mounted in theusual way so as to be readil tilted to allow the charge to be pouredfli'om the spout 5. The fuflnace mounting forms no part of thisinvention 60 and is illustrated in Figure 1 of the drawings of my priorapplication referred to.

My improvedfurnace bottom consists of an vouter shell 6 formed of metalplates, and a supporting layer of refractory material such 65 as basicor neutral bricks, a lining 7 of suitable mortar being interposedbetween the shell 6 and refractory layer 8.

The topmost or active layer 9, constituting the bottom or hearth of thefurnace which is 7 in direct contact with the charge, rests upon thelayer 8, and consists of carbonaceous material such as carbon, orgraphite, or a carbonaceous composition such as a mixture of graphitewith ferro-alloys, or other metals.

This layer 9 constituting the bottom or hearth proper is ofsubstantially uniform high conductivity throughout, and is electricallycon nected to the metallic shell 6 by means of a plurality of metalstrips or fins 10 secured at one end to the shell 6, and having theirother ends embedded in the layer 9 of carbonaceous material, such finsor strips extending through the refractory supporting layer 8.

The furnace is illustrated as having three electrodes a, b and 0,extending through the roof as usual, and connected to the ends of thesecondary winding of a three phase transformer w, the primaries w beingconnected in delta, while the secondariesg are connectrent not onlypasses from one electrode to the other, but may flow also from one ormore of the electrodes through the furnace bottom.

In order to vary the voltage and current flowing through the electrodesand furnace bottom, I preferably provide the primary windings with tapscontrolled by switches a: and also include in the primary circuitsuitable variable reactors w controlled by switches w. By manipulatingthe switches as and w, the voltage of the several phases maybecontrolled as desired.

When manufacturing and refining cast iron from iron or steel scrap orpig iron, it is often necessary to increase the percentageof carbon inthe charge, that is to carburize it. I have found that one veryeffective way of doing this is to mix with the cold scrap when it isintroduced into the furnace, a suitable amount of charcoal or coke. Whenthe charge is melted, this solid carbonaceous material floats on top ofthe molten charge and mixes -with the impurities to form a carburizingslag. I have found then, that when the charge is molten and in contactwith the above described carbonaceous bottom or hearth on one side andin contact with the carburizing slag on the other side, it can be veryeffecwood, thus causing ebullition of the molten mass.

A more effective method, however. is to bubble a gas or fluidtherethrough. The fluid employed may be either a non-oxidizing orreducing gas, such as nitrogen or hydrogen, under pressure, or it may bein the nature of a hydrocarbon, either gaseous or liquid. In-

the first case, the passage of the gas through the molten charge tendsto prevent oxidation or to reduce oxides present, while in either case aviolent bubbling or ebullition of the 'charge 1s produced, thusagitating the mass and brmging all parts thereof into intimate contactwith both the carbonaceous bottom and the carburizing slag.

Moreover, if a hydrocarbon or oil is employed, the gases or vaporstherefrom fill .the space in the furnace above the charge agitating themolten mass, and at the same by the a and themselves constitutecarbonaceous or carburizing material. Thus, by using'a fluid hydrocarbonfor bubbling through .the charge, it performs the double function oftime sup lying carbon which may be absorbed sametime. Thus, I may omitthe solid carbonaceous material and produce the carbur zing simply byagitating the molten mass in contact with my improved carbonaceoushearth, or I may agitate the mass by means of a fluid hydrocarbon asdescribed, or I may use an inert gas and employ solid carburizingmaterial in the form of a supernatant sla I h addition to itscarburizing function, my improved carbonaceous bottom is found to behighly resistant to both acid and basic slags.

In Figure 1 I have shown one method of forcing a fluid into and throughthe charge to agitate the same or to produce any other desired effect.

WVhere the furnace bottom is constructed, as described, of a layer ofcarbonaceous material supported upon a layer of refractory material andmortar, such bottom is, of course, quite porous, and I have discoveredthat it is sufficiently porous to permit streams of gas or other fluidto pass freely through .the pores thereof.

In order to introduce the gas or other fluid so that it can flow throughthe porous bottom as described, I tap the metallic shell 6 on which thebottom rests, and insert therein one end of a pipe 20, as clearly shownin Figure 1. To the other endof this pipe, a hose 16 may be attached.Gas or other fluid entering the pipe 20 under pressure will make its wayup through the pores of the several layers of material constituting thefurnace bottom and will bubble freely up through the molten charge, asindicated at 21. Owing to the fact that the gas has to permeate throughthe pores of the mass of carbonaceous and other material forming thefurnace bottom, such gas will be distributed or diffused and will passupward through the charge in widely scattered relatively small streams.

In Figure 2 I have shown means by which the incoming stream of gas orfluid may be even more widely distributed and diffused through thecharge than in the preceding figure.

Referring to Figure 2, it will be seen that I ploy a pipe 20 tappedthrough the metallic shell 6, as before, but in this figure I extend thepipe a short distance upwardly and mount upon its upper end atransversely extending cross pipe or manifold 22, having a series of perorations therein along the length thereof. This manifold is embedded inthe porous carbonaceous'or other material forming the upper la er of thefurnace bottom. It is obvious t at with this arran ement, the gasentering-the pipe 20 un er pressure will be distributed over a wide areaand will then be diffused as it permeates and asses up through theporous bottom and ally bubbles in small streams up through the moltencharge, as indicated at 21'.

. ent is:

, ing a bottom comprising a porous layer of igeaaaa 3 B virtue ofthefact that, in the arrangemenzs shown the gas or other fluid is broken upinto streams and difiused out the charge, it is caused to come mtointimate contact with all portions of the charge and the pipe-isprotected from the most intense heat of the furnace 4 being below orembedded in the material 0 the bottom.

While I have shown and described the pre- 10 ferred embodiment of myinvention, it is to I uisiltllerstood1 that various cianges in tlg:

., size, ape an arrangement 0 parts may resorted to without departingfrom the spirit 21f my invention or the scope of the subjoined Havingthus described my invention, what I claim and desire to protect byLetters Pat- 1. An electric furnace havcarbonaceous material in directcontact with the charge, and means for fo gas under pressure up throughthe pores 0 said layer and through 'the charge resting thereon :5whereby the charge is 'tated to bring it into intimate contact wi .thelayer of carbonaceous material. Y a 2. An electric metallurgical furnacehaving a bottom comprising a metallic shell and go a ayer of porouscarbonaceous materialsupported thereby, and means for causing gases tobubble up at a pluralia of points and be thus distributed through ccharge in a diffused state comprising a pipe tapp' said a shell andhaving at its end amamf fil-embedded in the porous material whereby thecharge is gtated to it into intimate contact wi the layer of,carbonaceousmaten I g 8. In an electricmetallurgical furnace havuig aporous the method 0 carburiain ilzlhe whi 6 comprises caus ng a m an orrescue to flew up through the t0 p inadiflusedstateand enceupthroughtheto agitate the charge and b it into intimate contact with the fluid bycarbon and with the carbonaceous bottom. 8 4. In an electricmetallurgical furnace'havo iIFaporouscarbonaceo' usbottom,themethod otreatinfthechargewhichcensistaincaus ingaflui underpreuuretoflowupthmughfie pores of such M as: "P '8 chargeandbringitintoinhrnatecontactwiththe carbonaceous bottom.

